Hardmetals are the composite materials which have carbides and a metal, e.g. Fe, Co, Ni etc., as binder phase. WC-Co is generally called hardmetal, since it has the best mechanical property. In Japan, hardmetal which has finished their cycle, have been recovered and reused or recycled. However, sludge produced from processing of hardmetal tools and its polishing has been discarded because there are difficulties to be treated. In addition, Japan depends on China for tungsten resource, developing recycling method of this sludge is necessary.
In this study, tungsten carbide (WC) was recovered from hardmetal sludge by mineral processing methods such as free-settling and liquid-liquid extraction. Free-settling method, which takes advantage of using the differences in sinking rate of WC and silica (SiO2) after separation by wet tower mill has been used. It was found that WC grade increased with increasing rotation speed of tower mill, but the recovery decreases. Whereas tungsten grade increased with decreasing milling time, the recovery of tungsten decreases. Another finding of this study is that WC grade increases and recovery decreases with increasing sinking time up to 3 h. When rotation speed is adjusted at 1500 rpm, milling time is kept at 1 h and sinking time is kept at 3 h, tungsten grade is increased up to 85.9 mass% from about 66.2 mass% and the recovery of tungsten is about 10 mass%. Moreover silica grade is decreased from 28.5 mass% to 5.9 mass%.
In case using liquid-liquid extraction, ultrasonic, cutter-mill and microwave were used for liberation. Grade and recovery of WC increased with increasing ultrasonic time. It takes more than 20 min for ultrasonication for improving WC grade to more than 90 mass%. By cutter-mill, WC grade decreased with increasing milling time, but the recovery increased. After 1 min WC grade was improved up to 89.9 mass% and the recovery was 23.8 mass%. WC grade was the highest when microwaving time was 5 min. Then, WC grade was 91.3 mass% and the recovery was 16.3 mass%.